Acyl carrier proteins (ACPs) are specifically involved in the shuttle of a nascent fatty acid from enzyme to enzyme during the complex process of fatty acid synthesis. However, they can be more generally viewed as being representative of a class of molecules that carry hydrophobic synthetic intermediates or more actively participate as a platform for synthetic modification of, hydrophobic molecules. Understanding the molecular details of acyl chain-protein interactions and protein-protein interactions in the ACP system can provide some of the basic knowledge necessary to understand the control of synthetic steps in a variety of biochemical processes. It is our goal to develop methods for the study of these interactions as well as elucidate the molecular details of the ACP system. Solution nuclear magnetic resonance (NMR) methods that exploit spin relaxation phenomena will be developed and combined with computer modeling protocols to give a structural and dynamic description of the acyl chain binding site on ACP from Escherichia coli. This description will be extended to ACP molecules from other species as well as ACPs produced by site specific mutagenesis in order to identify features which may dictate preferences for synthesis of certain fatty acids. Methods based on selection of signals from isotopically labeled sites will also be developed and applied to the study of interactions of ACPs with a key enzyme in anaerobic unsaturated fatty acid production. This effort should clarify the role protein-protein interactions may play in the control of fatty acid synthesis.